Environmental concerns and the need for fuel conservation has spurred the development of new hybrid propulsion systems for vehicles. Hybrid electric vehicle (HEV) powertrains for example, typically include electric traction motors, high voltage electric energy storage systems, and modified transmissions. Electric energy storage systems include batteries and ultra capacitors. Primary power units for these systems may include spark ignition engines, compression ignition direct injection (e.g., diesel) engines, gas turbines and fuel cells.
HEV powertrains are typically arranged in series, parallel or parallel-series configurations. With parallel-series arrangements, multiple motors operating in multiple operating modes sometimes require the use of several gear sets to effectively transmit power to the traction wheels. As a result, HEV powertrains often possess considerable effective inertia at the wheels compared to conventional ICE powertrains. This is due in part to the potentially large inertia of the hybrid motor devices, as well as the significant gearing from motor to wheels that is often employed.
Powertrains possessing relatively high effective inertias such as those of HEVs, result in certain problems that require solutions. For example, the application of braking force to the vehicle's traction wheels during a sudden braking event, may result in a very rapid angular momentum change in the powertrain. Specifically, a rapid deceleration of the traction wheels during braking results in a counter-torque being transmitted from the traction wheels back through the driveline. Because many of the components connected in the driveline have relatively large effective inertias at the wheels, the counter-torque produced by the braking event can produce relatively high reactive torque levels in the powertrain. This reaction torque is transmitted through the gearing mechanisms to the transmission housing, and can have deleterious effects on powertrain and driveline components, particularly under sudden braking conditions, such as when the vehicle's ABS system is activated.
Fluctuating driveline torques, which are transmitted through the vehicle's halfshafts, act to accelerate or decelerate the wheels, thereby potentially reducing the effectiveness of the vehicle's ABS system which is not designed to take into consideration dynamic powertrain reaction torque. Additionally, fluctuating driveline torque can produce noise, vibration and harshness (NVH) in the powertrain and driveline, and in some cases can even cause the vehicle's ABS to excite the vehicle powertrain at its natural frequency, thereby imposing additional undesirable stress on the powertrain.
Accordingly, there is a need in the art for a system for reducing or limiting reactive torque during operating conditions that impose high inertial forces on driveline components. The present invention is intended to satisfy this need.